Electromagnetic core construction and method



Oct. 3, 1961 A. E. FEINBERG Erm. 3,002,263

ELEcTRoMAGNETIc com; CONSTRUCTION AND METHOD Filed Dec. 14, 1954 j 2sheets-sheet 1 .54 44 J4 2 3,6 il 24K/gw@ w OC 3, 1951 A. ELFEINBERG`ETA. 3,002,263

ELEOTROMAGNETIO CORE CONSTRUCTION ANO METHOD Filed Dec. 14, 1954 2Sheets-Sheet 2 da? 2% .5x2 Q7 o Il" II (I l H" I' 54 lll lig M-Hljgylu?llU sa Wm Ill J m1 )L26 NW .Mgg l J@ N I" H; "5T N MMT if Il fw H" N lllNU" @W NN O .g4/ I i d i i 26 23 I M2311 U l 54 *,NII I NIH' NIW' lTltfINI,

' Q l T54 y-'p 2j) I2 0V' NH lll"I |lll l1' ONU il" Nllri Nl .6 d@ 5.3E? M30 ,L W" H l 4 u T @MNT 2 ||111N|M l:ll v .Q3/UT Q6 m) l 1 i L NI UVNH WO 9mm' .IH IIN Ww (2f) r 2 Wl' l] 7 22 23k, 24 fx-jf 25ml' (W22 $4 l'I j Mg TNNTORS. v .@iw @Wy IWW] v o United States Patent 3,002,263ELECTROMAGNETIC CORE CONSTRUCTION AND METHOD Albert E. Feinherg and PaulJ. Zerwes, Chicago, lll., as-

signors to Advance Transformer Co.,-Chicago, lll., a corporation ofIllinois Filed Dec. 14, 1954, Ser. No. 475,043 4 Claims. (Cl. 29-155.61)

This invention relates generally to a core construction forelectromagnetic devices such as transformers,l chokes and the like andin additionis concerned with a novel method of constructing a core ofthis type.

T'he invention is particularly applicable to shell type coresconstructed of laminations and in which there is a generally rectangularouter yframe or shell, having elongate sides and ends bridging thesides,and in addition there is a central windingleg which is disposed betweenthe ends extending the length of the linterior of the outer shell. Inpractice, a core of this structure is formed of a stack of laminations,each stamped out of silicon steel sheeting, heldV together by rivets orclamps. The diiculties which will be referred to occur principally inthe riveted cores but are not exclusive'thereto. In stamping theindividual laminations, the central winding leg lamination is punchedout of the blank simultaneously that the windows and outer frameportions are formed.

This may occur in a progressive sequence, with the var-y ious partsseparated by the punvchpress.

Thereafter, the frame laminations and winding leg laminations areseparately stacked and riveted together. The air gap or gaps are formedduring the punching operations, usually by a cutting operation known asshaving; This operation establishesvthe dimensions of the air gap orgaps, by means of which the eventual electrical characteristics of thedevice are established. The stacked winding leg is now provided withpre-woundvcoils that are slipped over the ends and positioned inalignment with the windows of the shell or frame stack, and thereafterthe ,assembled winding leg and coils are forced into the center of theframe or shell. 'Means are provided for positive alignment and seatingof the central winding leg. l

The above describes a method of producing the cores which is in commonuse. The further processing of the device is not involved in thisinvention.

Theoretically, since the central leg is re-iitted back into the openingformed when it wasy punched out, there should be no problem in soassembling the transformer or choke. Thus, predetermined gaps should notvary for any reason. This is not the case, however. In any shearing diewhich includes male and female portions, there must be clearance nomatter how little. The workpiece is therefore acted upon above and belowby shearing members which are moving along different parallel planes.rAv 'certain amount of cutting will take place, depending upon thesharpness of the die halves, but separation eventually occurs -along atear which extends diagonally from the contours` delined by the male dieportion to the contours` defined by vthe female'die portion. Consideringthe 'deiinition of the resulting pieces by the contours of the maleportion of the die, the punched out part will have an outward extension,and the perforated part will havean undercut.

Obviously, tting a single thickness of a winding leg lamination to asingle thickness of a iframe or shell lamination presents little or noproblem. The aligned members are assembled in the direction oppositethat in which 2 other during the pressing-in process, resulting ineither crushing of the edges' or deformation of one part or the other.

l tSince the stacked winding legs are engaged withy the shells only attheir ends, deformation which occurs during the pressing in of thecentral ywinding leg in practically all cases aiects the bridging endsof the shell, bowing them outward. 'This results in distortion of theunsupported elongate side walls with resultant changel in the gapdimensions. Thus the electrical characteris` tics of the device arechanged resulting in unsatisfae" tory performance of the transformer orchoke. Since die sharpness is any important factor and this varies, itis next to impossible to compensate for the change in gap thickness by,for example, shaving more material from gap forming extensions thannecessary if there were no distortion. n

It is the primary object of the invention to offset the abovedisadvantages otherwise inherent in the pressed-in shell type corestructure, by preventing distortion of the elongate sides of the coreduring the pressing-in of the winding leg.

A further object of the invention lies in the provision of means on thebridging ends of the outer shell or frame of the core to preventdistortion of the elongateI sides of the shells, and in connection withthis object various means comprise weakened portions whichwill ab l sorbor take on -any distorting strain without transmitting the same to thesides.

A still further object of the invention lies in the pro; vision of meanson the central winding leg to accom f plish the eliminationofrdistortion in the elongate sides,

they were rseparated during the punching operation. f

When a plurality of members are stacked, obviously there can be n'onesting in assembling, since the largest contour of the one must passthe smallest contour of the and specifically the said means may consistof a formalA tion shortening the length of said winding leg.

Still a further object of the invention lies in the provision of a novelmethod for accomplishing the shortening ofthe central winding leg. p

vMany other objects will occur to those skilled in the art as adescription of the invention proceeds in which;k

preferred embodiments of the invention have been de scribed in somedetail in order to comply with the patent statutes relating thereto. iApreferred embodiment of the method has also been described.

In the drawings: F-IG. 1 is a top plan view of a lamination for a shelltype core showing the manner in which the central winding leg portionmatingly engages with the shell or vframe portion and illustrating theconventional construction.

FIGS. 2 and? are diagrammatic views on a greatly enlarged scale showingin section what occurs in the punching operation during formation of thelamination of FIG. 1. FIG. 4 is an enlarged and exaggerated sectionalview showing the formation resulting along the edges of the parts of thelamination of FIG. 1 as a result of the punching operation.

FIGS. 5 and 6 are fragmentary plan views of the right hand ends oflaminations formed in accordance with the lamination of FIG. l0, thelatter illustrating a fourth form of the invention.

FIG. l1 is a sectional view along the line 11-11 of FIG. 10.

p As statedy above, the invention generally lies in preventing thedistortion of the elongate sides of the shell of the core'and therebymaintaining uniform gaps notwithstanding the growing" of the winding leglaminations during punching. In order to obtain a clear picture of theproblems solved attention is invited to FIGS. 1 through 4.

VFIG. l illustrates a lamination having a shell or frame parl A21 .ofrectangular construction, and a Vcentral. winding leg portion 2.2 whichis punched out ofthe same blank iorming lthe lamination 20, with itsends matingly engaged at 24 and 26 with the bridging ends 2S and 3l?`r..Spect.i.vely of the frame part 2l. The sides are desig- Hated 32 and34. Windows 36 and .38 are formed bctween the winding leg part 2.2 andthe frame part El for the reception of the coils (not shown). Thewindows are separated by juxtaposed spaced apart extensions 4t? and 42on the trame part 2l extending inwardly toward the outwardly extendingcounterparts da and 46 on the winding leg part 22. The separation formsthe gaps 48 and 50 the spacing of which is critical in mostelectromagnetic devices, since the reluctance of the shunt (that is the`combined extensions and gaps) atlects the reactive relationship betweenthe coils in the respective windows. The contours of the lamination 20are identical to the contours of the transformer which is manufacturedfrom a plurality of such laminations. Only the windings and fasteningmeans are -not shown. Thus, a predetermined number of parts 2l arestacked together in perfect alignment through the assistance of anindexing notch 52 0.11 im edge of the side 34, and riveted together.Rivet holes ,are shown at 54. The same number of parts 22 are alsostacked together and riveted, the rivet holes being shown at S6. Anindexing .hole 5S, part of which is in the bridging end 3c and part ofwhich is in the end of the winding leg part 22, serves the dual purposeof enabling proper alignment of the stack of winding leg parts 22 onewith the other, and indicating proper alignment of the assembled stackof parts 22 with the assembled stack of parts 2l. T he direction ofpressing-in of the winding leg into the frame is easily ascertained byreason of the burrs on both parts. The smooth surface of the winding legstack is to be inserted into the burred side of the frame part stack.

As described thus Afar, the construction is convention and the manner ofinserting 'the winding leg in the core is well-known. This method ofassembly gives rise to distortion of the sides 32 and 34 with attendantchanges inthe width of gaps 43 and Sil.

In FIG. 2 there is illustrated a blank or workpiece di? from which thelamination 2@ is to be punched. For the sake of description, it will bepresumed that the diagram illustrates in exaggerated dimension, theformation of the mating junction The workpiece dil is shown upon a lowerdie part 6l which has therein an opening 62 of the configuration of thewinding leg part 2.2 (either with or without the windows) This is thenthe female portion of the die. The punch 64 is shown poised over theworkpiece preparatory to being pressed upon the same and driven in tothe opening 62. Obviously, it has the same contours as the opening 62,but must be slightly smaller to permit such downward movement. Theclearance between die parts 6l and 64 is represented'by the space 66.

As the male die part 64 is driven downward, the sharp edges 58 and '70at first bite into the workpiece 6l), giving rise to pure shear surfaces72 and 74. This pure shearcontinues until the movement of the separatingparts of the workpiece 60 produces a stress across the edges 63 and 7l?that exceeds the tensile strength of the material. At this point thematerial yields, tearing across this diagonal along the line 76. Theexact position of this tear surface (it is actually a surface formedabout the edges of both of the separated pieces) depends upon manyfactors among which are: tensile strength of the steel, clearness 66 ofthe die parts, thickness of the workpiece 60, sharpness of the dies,type or workpiece padding, etc. The resulting pieces are illustrated inFIG. 4, forming the bridging end 28 and the end of the central leg part22.

Although the illustration oi FIG. 4 indicates that moving the two partstogether along the dotted lines 78 would probably not result in themating engagement of 4the parts of even a single lamination, it shouldbe appreciated that the drawing is somewhat exaggerated. Nornormallyitis not .difficult to force the two together. The purpose is to showthat the opening at 24 deiined by the edge 72 of the part 2l. is smallerthan the contour of the winding leg 22 defined by the edge 74. Certainlythe greatest distance between the mating junction 24-25 of the framepart 2111's substantially less than the greatest distance between theends of the winding leg part 74. When a stack 0f Winding leg laminationsis forced into the center of the ,frame something must give.

lt has been found .that the bridging ends 23 and 30 tend to bow outwardwhen the winding leg stack is pressed home. This is illustrated inexaggerated form by the broken lines and S2 in FIG. l. The resultingdistortion of the stacked `frame laminations is usually an inward bowingof the .elongate sides. This is exaggeratedly illustrated by the brokenlines 84 and 86. The inward bowing of the sides 32 and 34 of the framestack will materially decrease the width across gaps 48 and S0, and asexplained, the .amount of change of the gaps will not be controllable.Material changes in electrical characteristics of the transformer orchoke over original design will result from this alteration in gapdimension. Gap materials may in some way olset this change, but theforces applied are great and some change is bound to resultnotwithstanding.

ln any event, electrical changes result from such distortion which inmany cases are intolerable. The dithculties are aggravated Vwhere aclose toleranceof gaps is required for some particular characteristic ofthe electromagnetic device, and where more than one gapped shunt isaffected.

Generally the invention comprises providing some means to preventdistortion, and this takes two specic forms. In one form, there areprovided means which will absorb deformations caused when the windingleg is pressed home. In a second form, the winding leg is shortenedslightly during manufacture to compensate for its growing In FIGS. 5 and6, means are provided in the bridging end 3d capable of absorbingdeformation. In the lamination 12b of FIG. 5 there is a series of slots90 which are punched completely through the bridging end and generallyare arranged at right angles to the forces exerted when the winding leg22 is driven into place. Thus the slots are in an arc about the junction26. The slots provide a weakened portion in the bridging end which willbe somewhat crushed, perhaps slightly closing the slots when the windingleg is pressed home. Obviously if the distortion is all localized in thebridging end .30, there will be no distortion or bowing inward of thesides 32 and 34 and the gaps 48 and 50 will be unalected.

In the lamination 220 of FIG. 6, the slots 91 serve the same function asslots 90, but these are arranged geometrically different. A greateramount of weakening is provided at local arcas adjacent the innercorners of the end member 39. The function and operation is the same asslots 90.

In slotting the end 30, care must be taken to provide suicient iron tohandle the normal flux designed to thread Vthe core. Note that the widthof the end 30 is larger in FIGS. 5 and 6 than in FIG. 1 for the samedesign of electromagnetic device. Obviously the slotting decreases thecross section in places. The exact number and formation of slots is amatter of design, probably best ascertained by experiment, especially inview of the complex nature of the electrical characteristics of thiskind of apparatus. Care must be taken to avoid any areas where extremehigh lux density may result in saturation.

. In the lamination 320 illustrated in FIG. 7, instead of slotting theend 28, a shallow recess or notch 93 is formed along the outer edge ofthe end, so that when distortion occurs as it might in forcing thewinding leg home, the narrow strip 94 between the juncture 24and therecess 93 will tend to bow out or ex as indicated at 95 rather than -theentire bridging end 28. The s-ame salutary effects are obtained as inFIGS. 5 and 6. Y

In FIG. l0 there is illustrated a lamination 420 in which theconstruction is identical to that of the lamination of FIG. 1 with oneexception. There is a crimp 97 of simple formation which extends acrossthe central winding leg part 22 at the extensions 44 and 46. The crimpmay be of any configuration 30 that a stack of members 22 will nest, onesuch formation being triangular in cross section as shown in FIG. 1l.Obviously the crimp 97 will shorten the length of the winding leg 22slightly, and thereby offset the growth thereof during stamping. Thiscan prevent the distortion of the ends 28 and 30 during assembly ofstacks. Obviously there must be no crimp in the frame portion 21.

The crimp may be formed in the lamination 22 in any of a variety of waysand at any of the stages in the punching of the lamination, butfor highspeed production, a novel method of forming said crimp has been evolved.During the production of the lamination, at any suitable stage of thestamping operation, say during the first blanking step, or even Ibeforeblanking, if desired, the entire lamination is crimped across theposition of the shunt, that is, at the extensions 40, v42, 44 and 46.The crimp is more easily formed in a large and imperforate member.Thereafter, the crimps 97 in the sides 32 and 34 are attened. The iinalresult will -be the same as FIG. 10. The illustration in FIG. 8 showsthe lamination assembled together prior to the attening of the framepart 21. Obviously before this occurs, the, Winding leg part 22 dropsout of the press so that FIG. 9 illustrates the result of the iiatteningstep. By illustrating both parts 21 and 22 in FIG. 8 it is not intendedto imply that the entire lamination is completely punchedto shape beforethe crimps 97 and 97 are formed (although this might be done).Preferably the crimping should be done at a stage of the progressivepunching process at which there will be a minimum of distortion of theextensions forming the shunt and gaps.

The only reason for the crimp 97 being where shown in FIG. l0 is that itinterferes least with the insertion of the stacked winding leg into thecoils from opposite ends. The crimp 97 will, however, be quite small,and may be located in other places along the member 22 where convenienceand practicability permit. Obviously there may be several crimps, ifdesired.

What it is desired to secure by Letters Patent of the United States is:

l. The method of manufacturing a shell-type core for an electromagneticdevice in which the shell is formed from a plurality of preformedelectrical steel laminations stacked and secured together such that theshell is substantially rectangular to provide a pair of parallel,continuous side parts and a pair of continuous end parts bridging theside parts, and an elongate continuous central winding leg part fittinginto the interior of the shell with the extremities of the winding legintimately abutting said end partsand said winding leg kand sideL partshaving lateral extensions located with end faces thereof aligned andseparated to provide air gaps of predetermined dimension on oppositesides of the winding leg: said method comprising, stamping from a blankof electric-al steel individual laminations of which one corresponds tothe shape of the shell and the other corresponds to the shape of thewinding leg with said winding leg having been stamped from theblank'material between the bridging end parts of the shell lamination,forming at least a transverse crimp in the winding leg lamination toshorten same, said method being performed in a continuous processproviding a plurality of said individual laminations capable of being sostacked and secured together so that the crimped winding leg laminationsare accommodated on the interior of the shell laminations with thelinear distance between the end parts in the core remainingsublstantially equal to the linear distance between the end parts of theindividual shell laminations.

2. A method as described in claim 1 in which the crimp is located at thegaps.

3. A method as described in claim 1 in which said crimp is formedsimultaneously with the stamping out of the laminations from the blank.

i4. A method as described in claim 1 in which said crimp is formed inthe blank prior to stamping out of the laminations therefrom.

References Cited in the file of this patent UNITED STATES PATENTS WagnerJuly 5, 1927

